There are other translations of this pun in Act II, scene 4 of Romeo and Juliet. A pump is a light shoe. This definition is given in the Modern Text of Romeo and Juliet noted as such in an edition by John A Price. In this line,Romeo makes a pun on another use for "pink" which Mercutio uses in "I am the very pink of courtesy," with "pink" meaning Mercutio is a paragon of courtesy. Romeo plays on the word, saying "pink for pattern." In Romeo's line, "Pink"means to decorate in a perforated pattern."

Then, Mercutio says to keep jesting until the sole is worn out, punning on the words sole/soul; Romeo finishes the pun by saying,

O single-soled jest, solely singular for the singularness! (II,iv,64) [the pun is singular/unusual because of its silly simplicity]

As far as I know, this whole part of the play is a bunch of sexual puns and references. If you start a little farther back, you can see what is going on. Remember that in this part, Romeo has been away from Benvolio and Mercutio and they are saying he's been off with some girl (he has been with Juliet, but they don't know that).

So, Mercutio says he is the "pink of courtesy" and Romeo talks about a pink flower (allusion to female genitals). Then Romeo says his pump is well flowered (pump = male genitals and flower = female genitals. In addition, when a woman sleeps with a man for the first time, she is "deflowered."